<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script>
        /**
         * null 和 undefined 没有toString（）方法
         * @type {number}
         */
        // 转化为字符串
        let age = 11;//11
        let isShow = true;//true

        let ageStr = age.toString();//字符串11
        let s1 = isShow.toString();//字符串true

        console.log("age: " + typeof ageStr);//string
        console.log("isShow: " +typeof s1);//string

    </script>


</head>

<body>

</body>
</html>